The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems are used to deposit, etch and otherwise treat materials on substrates such as semiconductor wafers. Examples of etching processes include dry etching, vapor etching and/or wet etching. In some examples, one exposed material of the substrate may need to be etched selectively relative to one or more other exposed materials of the substrate.
In one application, silicon germanium (SiGe) needs to be etched selectively relative to silicon (Si), silicon nitride (SiN or Si3N4) and silicon dioxide (SiO2) to reveal Si nanowires. When selecting the etching process, selectivity between Si and SiGe is a primary consideration. However, there should also be sufficient selectivity to avoid material loss of other materials such as SiO2 and SiN. For example, material loss constraints for the 7 nm technology node (and smaller nodes where the Si nanowires may be used) should be less than 10-20 A for Si and SiO2 and less than 10 A for SiN.
When using dry etching processes, there is limited selectivity between SiGe and Si, which causes material loss on the Si nanowire. Vapor etching processes using hydrochloric acid (HCl) are slow and typically require a minimum of 30 minutes of processing time. Both techniques are followed by a wet process (such as a wet clean process using dilute hydrofluoric acid (HF)) and a channel oxidation process, which is typically performed using wet treatment with water and ozone.
When using wet etching processes to etch SiGe, it is very challenging to provide sufficient selectivity such that only SiGe is etched while Si, SiO2 and/or SiN are not etched. Existing chemistries for selectively etching SiGe relative to Si do not have sufficient selectivity relative to SiO2 and SiN.